Along with decrease in the size and the thickness of liquid crystal projectors and projection televisions, decrease in the size is also intended for the light source device assembled in such equipments, for example, by using a short arc type high pressure mercury vapor discharge lamp capable of obtaining a high luminance emission in a small size. However, since the high pressure discharge lamp of this type has no good starting performance in a cold state or re-starting performance in a hot state, it involved a problem that the rising time of the liquid crystal projector or the projection television was retarded.
Accordingly, while it is required to adopt means for enhancing the starting or re-starting performance of the lamp, since there is no extra space capable of affording an auxiliary starting electrode or the like in the emitting portion of a light emitting tube decreased in the size, starting of the lamp has been promoted by the means of increasing the starting voltage of the lamp and applying a high voltage pulse.
However, when the starting voltage of the high pressure discharge lamp is increased, since a sufficient insulation distance has to be ensured between wirings constituting a lighting circuit, this involves a problem of increasing the size of the lighting circuit to enlarge the installation space for the light source device, and the size of the liquid crystal projector, etc., can not be decreased.
Further, in a case where the pulse voltage of the high voltage pulse applied to the starting voltage is high, noises that cause erroneous operation to the electric circuits such as in a liquid crystal projector may possibly be generated.
In view of the above, for preventing the generation of noises and avoiding increase in the size of the lighting circuit, means for mounting a lamp starting trigger wire 41 capable of starting the lamp at a relatively low voltage to a high pressure discharge lamp 40 has been proposed (refer to patent documents 1, 2, and 3) as shown in FIG. 15.
The high pressure discharge lamp 40 has a constitution in which a pair of electrode assemblies 42R,42L each having electrode 43 connected with a power supply lead 45 by way of a metal foil 44 comprising a molybdenum foil are inserted to both ends of a light emitting tube 46 comprising a quartz glass tube so as to oppose the electrodes 43 to each other in a light emitting portion 47 formed in the central portion of the light emitting tube 46 and fixed to a pair of sealing portions 48R,48L for air tightly sealing the both ends thereof.
Generally, the trigger wire 41 mounted to the high pressure discharge lamp 40 by winding and securing at one end 41a directly to the outer periphery of the power supply lead 45 of the electrode assembly 42R protruded from the sealing portion 48R on one side and wound at the other end 41c in a looped shape around the outer periphery of the sealing portion 48L on the other side. Although not illustrated, it also includes a constitution in which a portion of the trigger wire 41 wired to the sealing portion 48L is spirally wound around lengthily along the outer periphery of the sealing portion 48L or in which two front and back loop portions are formed on the side of the other end 41c of the trigger wire 41 and both of the loop portions are wound separately on the side of the light emitting portion 47 and on the side of the metal foil 44 of the sealing portion 48L respectively (refer to patent document 4).
Further, for preventing that quartz as the material for the light emitting tube 46 is damaged by positive ions drawn to the trigger wire 41, thereby lowering the mechanical strength, it has been considered that the intermediate portion 41b of the trigger wire 41 is preferably not in contact with the surface of the light emitting tube 46 but mounted in a state spaced apart at least by several mm from the surface thereof (refer to patent documents 1 and 2).
[Patent document 1]
Publication of JP-A No. 2004-335457
[Patent document 2]
Publication of JP-A No. Hei 9-265947
[Patent document 3]
Publication of JP-A No. Hei 8-87984
[Patent document 4]
Publication of JP-A No. 2003-526182
However, according to the knowledge of the present inventors, it is confirmed that when the trigger wire 41 in the state as illustrated by a solid line being spaced apart from the surface of the light emitting tube 46 is brought closer to the surface of the light emitting tube 46 as illustrated by a broken line FIG. 15, the starting or re-starting performance can be improved. Further, in the liquid crystal projector and the projection television, since the length of the rising time dominates the value of commercial products, the high pressure discharge lamp used as the light source for them is particularly required to have good stating or re-starting performance and when the importance is attached most to the starting or re-starting performance thereof, the trigger wire 41 is preferably brought closer to the surface of the light emitting tube 46 to mount the intermediate portion 41b in a state in contact with the surface of the light emitting portion 47 of the light emitting tube 46 as illustrated by a broken line FIG. 15.
Then, when the present inventors have conducted a test for practical use on the high pressure discharge lamp 40 in which the intermediate portion 41b of the trigger wire 41 is in contact with the surface of the light emitting portion 47 of the light emitting tube 46 as illustrated by the broken line in FIG. 15, since the intermediate portion 41b of the trigger wire 41 is heated to a high temperature of about 900° C. upon lighting up of the lamp, to cause elongation due to thermal expansion and spaced apart from the surface of the light emitting portion 47 having a smaller heat expansion coefficient than that of the trigger wire 41, this leads to the result that the re-starting performance in the hot state is not preferred.
Particularly, when the trigger wire 41 is in a state in contact with the surface of the light emitting portion 47 not only at the intermediate portion 41b but also at the other end 41c that is wound around the outer periphery of the sealing portion 48L, elongation by thermal expansion of the other end portion 41C is also added to increase the extent that the intermediate portion 41b is spaced apart from the surface of the light emitting portion 47. In addition, although the trigger wire 41 mounted to the high pressure discharge lamp 40 is fixed by being wound and secured at one end 41a to the lead 45, since the other end 41c is not fixed but being merely wound around the outer periphery of the sealing portion 48L, it entirely causes slack or distort tending to be spaced apart from the surface of the light emitting tube 46. In addition, if slacking or distortion should occur, since the intermediate portion 41b does not return to the state in contact with the surface of the emitting portion 47 even when the trigger wire 41 is cooled and shrunk after putting off the lamp, the starting performance in the cold state is also lowered.
Further, as a light source device for a liquid crystal projector or a projection television, while a lamp having a reflection mirror in which a high pressure discharge lamp 40 is provided integrally with a concave reflection mirror 49 by fixing a sealing portion 48L on one side to the bottom portion 50 of the reflection mirror 49 is general, there is also such a constitution that an auxiliary-reflection mirror 52 is mounted to the sealing portion 48R for reflecting the light emitted from the light emitting portion 47 of the light emitting tube 46 toward the opening 51 of the concave reflection mirror 49 to the side of the light emitting portion 47 for improving the efficiency of utilizing the light of the high pressure discharge lamp 40, as shown in FIG. 16.
However, since the trigger wire 41 mounted to the high pressure discharge lamp 40 having the auxiliary-reflection mirror 52 mounted thereto cannot but be wired so as to pass the outside of the auxiliary-reflection mirror 52 as an obstacle while avoiding the same (refer to patent document 5), it is impossible to improve the starting or re-staring performance by approaching the trigger wire 41 to the surface of the light emitting tube 46.
[Patent document 5]
Publication of JP-A No. 2005-283706